Hello Hartmut: > > The scaling factor for VREFP is 3.0/4096, not 1.0/4096; fix this to get > > correct readings. > > I just had a look at the datasheet [1], table 3-1 on page 37, and > get the feeling > that this scaling factor also applies to the VREFN channel. What is > your opinion? > > [1] http://www.xilinx.com/support/documentation/user_guides/ > ug480_7Series_XADC.pdf The table provides the following references: - VREFP: Figure 2-10, transfer function 3*unsigned(code)/4096 - VREFN: Figure 2-3, transfer function 1*unsigned(code)/4096 The table also says about VREFN: "The supply sensor is also used to measure VREFN, thus 1 LSB = 3V/4096." I agree that this is not consistent (by Figure 2-3, 1 LSB = 1V/4096), but I didn't have the means to check which version is true as VREFN is close to 0V either way. The situation is simpler for VREFP as UG480 is unambiguous here, and by measuring the actual voltage we can tell 1.25V and 0.41V easily apart, even when taking some measurement errors into account. In other words, we have to use the factor 3 to get correct results for VREFP (thus the patch), while either factor returns plausible results for VREFN. I would suggest opening a webcase with Xilinx for clarification, and adding another patch for VREFN if the factor 3 is confirmed. Can you do this? If not, I can take care of it, but it may take a while as I am pretty busy at the moment. Best regards, Thomas -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
